This is an open label, two-center trial in which 10 mg of idoxifene will be administered daily for two years to postmenopausal women. Each woman will act as her own control and comparisons will be made between the histomorphometric parameters of the bone biopsy at baseline and during treatment. Thin needle bone biopsies of the iliac crest will be performed at baseline and at yearly intervals. Before each biopsy the patient will take a short course of tetracycline at defined intervals to provide bone labeling for determination of dynamic histomorphometry values. All biopsies will be processed and sectioned to provide a preliminary assessment of the quality of the tissue. This analysis will determine whether or not the biopsy will yield sufficient information to calculate the activation frequency. The biopsies will be fully evaluated by a blinded reviewer, who is not aware of the chronological order of the biopsies, at the end of the study. The hypothesis being tested is that idoxifene will have estrogenic effects on bone histomorphometry in postmenopausal women with high bone turnover without having adverse effects on bone quality.